The invention relates to methods of providing and controlling electromagnetic flux in dispensing refined metal. In particular, the invention relates to providing, controlling, and concentrating electromagnetic flux during dispensing of refined metal using a copper guide tube.
Electroslag refining is an exemplary metal refining process that is used to melt and refine a wide range of alloys, including but not limited to superalloys, for removing various impurities therefrom. U.S. Pat. No. 5,160,532, issued to Benz et al., discloses an electroslag refining apparatus that is assigned to the Assignee of the present invention, General Electric. Other ESR structure are set forth in several U.S. patents issued to the Assignee of the present invention, General Electric, including U.S. Pat. Nos. 5,310,165; 5,325,906; 5,332,197; 5,348,666; 5,366,206; 5,472,097; 5,649,992; 5,649,993, 5,683,653, 5,769,151; 5,809,057; and 5,810,066, the contents of each are incorporated herein.
In general, an electroslag refining apparatus comprises an ingot being connected to a power supply, for example one of an alternating or direct current power supply. The ingots comprise unrefined alloys that may include various defects or impurities, which are desired to be removed during the refining process to enhance its metallurgical properties, including, but are not limited to, oxide cleanliness, grain size and microstructure. The ingot forms a consumable electrode that is suitably suspended in a water-cooled crucible, which contains a slag corresponding with the alloy being refined. The slag is heated by passing an electrical current from the consumable electrode through the slag into the crucible. The slag is maintained at a suitable high temperature for melting the lower end of the consumable electrode into an ingot melt. As the consumable electrode melts, a refining action takes place with oxide inclusions in the ingot melt being exposed to the liquid slag and dissolved therein. Refined liquid melt of the ingot melt falls through the slag by gravity, which may be augmented or diminished by electromagnetic forces or other means. The liquid refined melt is collected in a liquid melt pool at the bottom of the crucible. The slag, therefore, effectively removes various impurities from the melt to effect the refining thereof. The refined melt may be extracted from the crucible by an induction-heated, segmented, water-cooled copper guide tube. The refined melt extracted from the crucible thus provides a liquid metal source for various solidification processes including, but not limited to, powder atomization, spray deposition, spray forming, investment casting, melt-spinning, nucleated-casting, strip casting, and slab casting.
In the above-described electroslag refining apparatus, the crucible can be formed of copper, and is typically water-cooled to form a solid slag and/or metal skull on its surface. The solid slag or metal skull bounds the liquid slag and prevents damage to the crucible itself. The bottom of the crucible typically includes a water-cooled, cold hearth, which can be formed of copper, against which a solid skull of the refined melt forms for maintaining the purity of the collected melt at the bottom of the crucible. A discharge guide tube assembly below the hearth can also be formed of copper. The discharge guide tube assembly is often segmented and water-cooled and allows the formation of a solid skull of the refined melt for maintaining the purity of the melt as it is extracted from the crucible. The skulls can prevent contamination of the ingot melt from contact with the parent material of the crucible.
The electroslag refining apparatus also may include a plurality of water-cooled induction heating electrical conduits that surround the discharge guide tube. The conduits inductively heat the melt and the discharge guide tube can control the discharge flow rate through the discharge guide tube. Accordingly, the thickness of the skull formed around the discharge orifice may be controlled and suitably matched with melting rates of the consumable electrode for obtaining a substantially steady state production through the discharge guide tube.
The discharge guide tube and cold hearth of some electroslag refining apparatuses are generally structurally complex, and generally comprise a plurality of fingers or segments, which are surrounded by the induction heating electrical conduits. These induction heating electrical conduits are often single piece units that are typically provided with a set configuration to conform with the configuration of the discharge guide tube. The configuration is provided to define a gap between the induction heating electrical conduits and the discharge guide tube. This configuration is suitable for heating the melt in and about the discharge guide tube in electroslag refining applications. However, if one or both of the induction heating electrical conduits and discharge guide tubes are moved with respect to one another, the gap therebetween changes due to the single-piece configuration of the induction heating electrical conduits. Therefore, the heating of the melt in and about the discharge guide tube in electroslag refining applications may be influenced, often detrimentally.
The above-described electrical conduits generate, an electromagnetic field, and an associated electromagnetic flux within the discharge guide tube, generating heat in the liquid metal stream flowing therethrough. The intensity of the generated electromagnetic field and resulting electromagnetic flux is typically related to the heating capability of the guide tube apparatus. As the electromagnetic flux intensities increase, the heating capability within the discharge guide tube increases. A high field intensity and electromagnetic flux, and resultant high heating capability in a guide tube apparatus, is often desirable for creating an initial stream of metal, melting any undesired solid metal within the electroslag refining apparatus, and superheating the stream flowing through the discharge guide tube. The electromagnetic flux intensity in the electroslag refining apparatus can be enhanced by providing at least one of a high applied voltage in the electrical conduits and an increased number of induction heating elements disposed about the electroslag refining apparatus.
Further, the configuration and structure of the electroslag refining apparatus can limit a number of induction heating elements. Further, the current amount is limited by the configuration and structure of the induction heating elements and an availability of electrical energy. Thus, the electroslag refining apparatus may be limited in its the capability to control or enhance the electromagnetic flux and thus the flow in the discharge guide tube and the heating of the metal flowing therethrough.
Accordingly, a need exists to provide a method for controlling electromagnetic flux concentration in dispensing refined metal, for example, but not limited to, dispensing refined metal from electroslag refining apparatuses.
In an aspect of the invention, method for controlling electromagnetic flux concentration in a discharge guide tube for a metal refining apparatus is provided. The discharge guide tube comprises a base plate, an extension, a central orifice that extends through the extension from a source of metal to an outlet in the discharge guide tube for directing a stream of metal therethrough, and an interior discharge guide tube flux concentration configuration; an induction heater system that generates an electromagnetic field in the discharge guide tube, the induction heater system being disposed on the extension with a gap defined therebetween, the induction heater system and the discharge guide tube being capable of relative vertical movement and subsequent positions with respect to each other with the gap being essentially constant. The method for controlling electromagnetic flux concentration comprises providing current to the induction heater system; generating an electromagnetic field resulting from the step of providing current; and directing an electromagnetic flux to the central orifice at locations defined by the interior discharge guide tube flux concentration configuration in response to the generating an electromagnetic field. The step of generating an electromagnetic flux also generates heat and the step of generating heat provides a control of the flow of the stream of metal in its liquidus condition. The electromagnetic field is applied at a substantially constant level regardless of the relative vertical movement and subsequent positions between the induction heater system and the discharge guide tube.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.